Pumping mechanism with plunger

ABSTRACT

A pumping mechanism includes a barrel assembly having a plunger bore. The plunger bore has a longitudinal axis. The pumping mechanism also includes a plunger configured to slide within the plunger bore parallel to the longitudinal axis. The pumping mechanism further includes a push rod separate from the plunger. The push rod is configured to move away from the plunger to be spaced from the plunger, and the push rod is further configured to move within the plunger bore to push the plunger.

TECHNICAL FIELD

The present disclosure relates generally to a pumping mechanism, andmore particularly, to a pumping mechanism with a plunger.

BACKGROUND

Gaseous fuel powered engines are common in many applications. Forexample, the engine of a locomotive can be powered by natural gas (oranother gaseous fuel) alone or by a mixture of natural gas and dieselfuel. Natural gas may be more abundant and, therefore, less expensivethan diesel fuel. In addition, natural gas may burn cleaner in someapplications.

Natural gas, when used in a mobile application, may be stored in aliquid state onboard the associated machine. This may require thenatural gas to be stored at cold temperatures, e.g., about −100 to −162°C. The liquefied natural gas is then drawn from the tank by gravityand/or by a boost pump, and directed to a high-pressure pump. Thehigh-pressure pump further increases a pressure of the fuel and directsthe fuel to the machine's engine. In some applications, the liquid fuelmay be gasified prior to injection into the engine and/or ignited bydiesel fuel (or another fuel or ignition source) before combustion.

One problem associated with pumps operating at cryogenic temperaturesinvolves heat transfer to the fuel while inside the pump. In particular,moving components of the pump create heat through friction, and thisheat (as well as ambient heat and/or heat from lubrication inside thepump) can be conducted to the fuel. If the fuel absorbs too much heatwhile in the pump, the fuel may gasify too early, thereby disruptingdesired operation of the pump and/or the engine.

One attempt to improve pumping of a cryogenic liquid is disclosed inU.S. Pat. No. 2,837,898 (the '898 patent) that issued to Ahistrand onJun. 10, 1958. In particular, the '898 patent discloses a swashplatetype system having three pumping elements disposed within a container.The container is divided into a liquid chamber and a gas chamber.Connecting rods extend through a neck of the container and the gaschamber to each of the three pumping elements to reciprocatingly drivethe pumping elements. A storage tank feeds liquid fuel to a bottom ofthe liquid chamber. The liquid chamber is connected to the gas chambervia a connecting line, and a gas return line returns vapors and/orliquid fuel from the gas chamber to a top of the storage tank. The levelof liquid fuel in the gas chamber is self-adjusting, and remains abovethe three pumping elements.

While the system of the '898 patent may reduce some heat transfer to theliquid fuel by positioning the gas chamber above the pumping elements,it may still be less than optimal. In particular, the '898 patent mayrequire a large container to accommodate both of the liquid and gaschambers, which may be difficult to package in some applications andalso expensive. Further, the pumping elements themselves may generateheat that is still conducted into the liquid.

The disclosed fluid system is directed to overcoming one or more of theproblems set forth above.

SUMMARY

In one aspect, the present disclosure is directed to a pumping mechanismincluding a barrel assembly having a plunger bore. The plunger bore hasa longitudinal axis. The pumping mechanism also includes a plungerconfigured to slide within the plunger bore parallel to the longitudinalaxis. The pumping mechanism further includes a push rod separate fromthe plunger. The push rod is configured to move away from the plunger tobe spaced from the plunger, and the push rod is further configuredplunger.

In another aspect, the present disclosure is directed to a pumpincluding a reservoir configured to store a fluid and at least onepumping mechanism at least partially disposed in the reservoir. The atleast one pumping mechanism includes a barrel assembly having a plungerbore. The plunger bore has a longitudinal axis and is fluidly connectedto the reservoir. The at least one pumping mechanism also includes aplunger configured to slide within the plunger bore along thelongitudinal axis in a first direction and in a second directionopposite the first direction. The at least one pumping mechanism furtherincludes a push rod separate from the plunger, and the push rod isconfigured to move away from the plunger to allow the plunger to move inthe first direction. The push rod is further configured to move withinthe plunger bore to push the plunger in the second direction to directthe fluid to a discharge passage of the pump.

In another aspect, the present disclosure is directed to a fluid systemincluding a storage tank configured to store a fluid, a pump fluidlyconnected to the storage tank to receive the fluid, and a boost pumpconfigured to pressurize the fluid to communicate the fluid from thestorage tank into the pump. The pump includes a reservoir configured tostore the fluid pressurized by the boost pump and at least one pumpingmechanism at least partially disposed in the reservoir. The at least onepumping mechanism includes a barrel assembly including a plunger bore.The plunger bore has a longitudinal axis and is fluidly connected to thereservoir. The at least one pumping mechanism also includes a plungerconfigured to slide within the plunger bore along the longitudinal axisin a first direction and in a second direction opposite the firstdirection, and a push rod separate from the plunger. The push rod isconfigured to move away from the plunger to allow the plunger to move inthe first direction due to a pressure from the fluid pressurized by theboost pump. The push rod is also configured to move within the plungerbore to push the plunger in the second direction to direct the fluid toa discharge passage of the pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a fluid system including a pump,according to an exemplary embodiment;

FIG. 2 is a perspective view of a manifold of the pump of FIG. 1;

FIG. 3 is a top view of the manifold of the pump of FIG. 1;

FIG. 4 is a cross-sectional view of the pump of FIG. 1;

FIG. 5 is a cross-sectional view of a pumping mechanism of the pump ofFIG. 1; and

FIG. 6 is another cross-sectional view of the pump of FIG. 1.

DETAILED DESCRIPTION

Reference will now he made in detail to exemplary embodiments, which areillustrated in the accompanying drawings. Wherever possible, the samereference numbers will be used throughout the drawings to refer to thesame or like parts.

FIG. 1 illustrates a fluid system 10 that may be used to supply apressurized fluid. In an embodiment, the fluid system 10 may be a fuelsystem used to provide a pressurized fuel, such as a cryogenic fluid, toa power source, such as an engine 12, which may be a gaseous fuelpowered internal combustion engine. It is understood, however, that thedisclosed embodiments may apply to other engines that utilize gaseousfuel.

In an embodiment, the fluid system 10 may include a storage tank 14, aboost pump 16, and a pump 100. The storage tank 14 may store fuel as afluid, e.g., a liquid fuel (LNG) and/or gaseous fuel. The boost pump 16may pump the fuel, e.g., LNG, from the storage tank 14 to the pump 100and may generate a low-pressure fluid discharge for supplying to thepump 100. The pump 100 may be mechanically driven by an external sourceof power (e.g., a combustion engine, such as the engine 12, or anelectric motor) to generate a high-pressure fluid discharge forsupplying to the engine 12. Thus, the boost pump 16 may be alow-pressure pump, and the pump 100 may be a high-pressure pump. Thepump 100 may discharge the fuel, e.g., LNG, intended to be consumed bythe engine 12. It is contemplated, however, that the pump 100 mayalternatively or additionally be configured to pressurize and dischargea different fluid, such as a different cryogenic fluid, if desired. Forexample, the cryogenic fluid may be liquefied helium, hydrogen,nitrogen, oxygen, or another fluid known in the art.

An inlet line 30 may fluidly connect the boost pump 16 to the pump 100to direct fuel, e.g., LNG, pressurized by the boost pump 16 to the pump100. One or more devices for controlling the flow of fuel may bedisposed in the inlet line 30, such as a shut-off valve 32 to stop theflow of fuel to the pump 100. A filter 34 may be disposed in the inletline 30 to filter the fuel directed to the pump 100. One or more sensors36 or monitoring devices may be disposed in the inlet line 30 todetermine at least one parameter relating to the fuel directed to thepump 100, such as temperature and/or pressure, e.g., to control thefluid system 10. For example, the sensor 36 may monitor the pressure ofthe fuel to control the boost pump 16 to ensure that the boost pump 16is pressurizing the fuel to a desired pressure or range of pressures. Avent valve 38 may be disposed in the inlet line 30 to permit the removalof fuel from the inlet line 30, e.g., after shutting down the fluidsystem 10 and/or the engine 12. The shut-off valve 32 and the vent valve38 may be manually operated by an operator.

A discharge line 40 may fluidly connect the pump 100 to the engine 12 todirect fuel pressurized by the pump 100 to the engine 12. One or moredevices for controlling the flow of fuel to the engine 12 may bedisposed in the discharge line 40. In addition, a heater 42 may bedisposed in the discharge line 40 to convert the fuel, e.g., LNG, to agaseous state. An accumulator 44 may be disposed in the discharge line40 downstream of the heater 42 to store the gaseous fuel, e.g., beforestarting the engine and/or when priming the pump 100. The accumulator 44may serve as a reservoir to ensure that fuel of adequate pressure isavailable to the engine 12. In addition, an injection system. (notshown) may deliver the gaseous fuel to the engine 12.

A leakage line 50 and a bypass line 60 may also fluidly connect the pump100 to the storage tank 14 to direct fuel from the pump 100 to thestorage tank 14, as described below. As shown in FIG. 1, the leakageline 50 and the bypass line 60 may combine before connecting to thestorage tank 14. A regulating valve 62 may be disposed in the bypassline 60 to control an amount of fuel, e.g., liquid and/or gaseous fuel,directed from the pump 100 to the storage tank 14. In an embodiment, theregulating valve 62 may control the amount of fuel based on a pressureof the fuel in the storage tank 14, e.g., to be within a range of thepressure of the fuel in the storage tank 14, such as withinapproximately 5 to 1,000 kPa. Alternatively, in place of the regulatingvalve 62, the bypass line 60 may include an orifice of a fixed size forcontrolling the amount of fuel directed from the pump 100 to the storagetank 14 via the bypass line 60. One or more sensors 64 or monitoringdevices may be disposed in the bypass line 60 to determine at least oneparameter relating to the fuel in the bypass line 60, such astemperature and/or pressure, e.g., to control the fluid system 10. Forexample, the sensor 64 may monitor the temperature of the fuel in thebypass line 60 to control when to start and/or stop priming the pump100.

A pressure relief valve 66 may be fluidly connected to the bypass line60 to release pressure to the atmosphere in the event that the pressureof the fuel in the bypass line 60 exceeds a threshold. For example, whena component in the fluid system 10 fails (e.g., if the regulating valve62 gets stuck in the closed position), then the pressure may increasehigh enough to break a component in the fluid system 10 and/or cause afailure in the fluid system 10. Also, if the fluid system 10 is shut offwhen there is liquid fuel present in the bypass line 60 and the liquidfuel is heated, the pressure in the bypass line 60 may increase highenough to break a component in the fluid system 10 and/or cause afailure in the fluid system 10.

The pump 100 may be generally cylindrical and divided into two ends. Forexample, the pump 100 may be divided into an input or warm end 102, inwhich a driveshaft 104 is supported, and an output or cold end 106. Thecold end 106 may be further divided into a reservoir section 120 and amanifold 200. Each of these sections may be generally aligned with thedriveshaft 104 along a common axis 110, and connected end-to-end. Withthis configuration, a mechanical input may be provided to the pump 100at the warm end 102 (i.e., via the driveshaft 104), and used to generatea high-pressure fluid discharge at the opposing cold end 106. In mostapplications, the pump 100 will be mounted and used in the orientationshown in FIG. 1 (i.e., with the reservoir section 120 being locatedgravitationally lower than the manifold 200).

The warm end 102 may be relatively warmer than the cold end 106.Specifically, the warm end 102 may house multiple moving components thatgenerate heat through friction during operation. In addition, the warmend 102 may be connected to the power source, and therefore may resultin heat being conducted from the power source into the pump 100.Further, if the pump 100 and the engine 12 are located in closeproximity to each other, air currents may beat the warm end 102 viaconvection. Finally, fluids (e.g., oil) used to lubricate the pump 100may be warm and thereby transfer heat to the warm end 102. In contrast,the cold end 106 may continuously receive a supply of fluid having anextremely low temperature. For example, LNG may be supplied to the pump100 from an associated storage tank storing LNG at temperatures of,e,g., about −100 to −162° C. In some embodiments, LNG may be supplied tothe pump 100 at less than about −140° C. or less than about −120° C.This continuous supply of cold fluid to the cold end 106 may cause thecold end 106 to be significantly cooler than the warm end 102. If toomuch heat is transferred to the fluid within the pump 100 from the warmend 102, the fluid may gasify within the cold end 106 prior to dischargefrom the pump 100, thereby reducing an efficiency of the pump 100.

The pump 100 may be an axial plunger type of pump. In particular, thedriveshaft 104 may be rotatably supported within a housing (not shown),and connected at an internal end to a load plate 112. The load plate 112may be oriented at an oblique angle relative to the axis 110, such thatan input rotation of the driveshaft 104 may be converted into acorresponding undulating motion of the load plate 112. A plurality oftappets (not shown) may slide along a lower face of the load plate 112,and a push rod 114 may be associated with each tappet. In this way, theundulating motion of the load plate 112 may be transferred through thetappets to the push rods 114 and used to pressurize the fluid passingthrough the pump 100. A resilient member (not shown), for example a coilspring, may be associated with each push rod 114 and configured to biasthe associated tappet into engagement with the load plate 112. Each pushrod 114 may be a single-piece component or, alternatively, comprised ofmultiple pieces, as desired. Many different shaft/load plateconfigurations may be possible, and the oblique angle of the driveshaft104 may be fixed or variable, as desired.

The reservoir section 120 may include a close-ended jacket 122 connectedto the manifold 200 (e.g., to a side of the manifold 200 opposite thewarm end 102), by way of a gasket 126 and/or pressure-assisted seal, toform an internal enclosure or reservoir 124. The reservoir 124 may be influid communication with the inlet line 30 via the manifold 200, asdescribed below. In the disclosed embodiment, the jacket 122 may beinsulated, if desired, to inhibit heat from transferring inward to thefluid contained therein.

The manifold 200 may perform several different functions. In particular,the manifold 200 may function as a guide for the push rods 114, as amounting pad for one or more pumping mechanisms 300, and as adistributor/collector of fluids for the pumping mechanism(s) 300. In theexemplary embodiment, the pump 100 has five pumping mechanisms 300, butit is understood that there may be more or fewer than five pumpingmechanisms 300. The pumping mechanisms 300 may be connected to themanifold 200 and extend into the reservoir 124.

FIGS. 2 and 3 illustrate the manifold 200, according to an exemplaryembodiment. The manifold 200 may include a first side 202 and a secondside 210 opposite the first side 202. A peripheral surface 220 of themanifold 200 may extend between the first side 202 and a second side210. In the embodiment shown, the manifold 200 has a circular profilewhen viewed from the top view of FIG. 3, but it is understood that themanifold 200 may have a non-circular profile, such as a square,rectangular, polygonal, or irregular profile.

The second side 210 may include a base 212 connected to the warm end102, and the first side 202 may include a raised portion 204 extendingfrom the base 212. The raised portion 204 may be at least partiallyinserted into the open end of the jacket 122, as shown in FIGS. 1, 4,and 5, to assist in providing a seal between the jacket 122 and themanifold 200.

The raised portion 204 may include a surface 205 that faces thereservoir 124 when the manifold 200 is connected to the reservoirsection 120. On the side of the base 212 opposite the raised portion204, the base 212 may include a surface 214 facing the warm end 102 ofthe pump 100. Surfaces 205 and 214 may be located on opposite sides ofthe manifold 200 relative to the axis 110 when disposed in the pump 100.

The base 212 may also form a flange that extends outward from aperiphery of the raised portion 204. One or more mounting bores 216,e.g., twelve mounting bores 216 as shown in FIGS. 2 and 3, may be formedon the flange and may receive one or more fasteners 218. The flange ofthe base 212 may be connected to a flange of the jacket 122 usingfasteners 218, with the gasket 126 sandwiched between the flanges.

The manifold 200 may include a plurality of push rod guide bores 206configured to receive the respective push rods 114. The push rod guidebores 206 may extend through surface 205, and may extend betweensurfaces 205 and 214 of the manifold 200. As shown in FIG. 3, the pushrod guide bores 206 may be disposed radially around the center ofsurface 205, e.g., radially spaced at generally equal intervals.

The manifold 200 may include a plurality of passages configured tofluidly communicate fuel between the storage tank 14, the pump 100, andthe engine 12. In an embodiment, the manifold 200 may have formedtherein a common inlet passage 230, a high-pressure discharge passage240, a leakage passage 250, and a bypass passage 260. It should be notedthat the inlet passage 230, the discharge passage 240, the leakagepassage 250, and the bypass passage 260 are not shown in any particularorientation in FIGS. 1-3.

The inlet passage 230 may include an inlet 232 that may be fluidlyconnected to the inlet line 30 so that the inlet 232 may receive fuelpumped from the storage tank 14 using the boost pump 16. The inlet 232may be disposed on the peripheral surface 220 of the manifold 200, asshown in FIGS. 2, 3, and 6. Alternatively, the inlet 232 may be disposedon any surface of the manifold 200 outside surface 205, such as surface214. The inlet passage 230 may also include an outlet 234 that mayextend through surface 205 so that the fuel pumped from the storage tank14 may be supplied to the reservoir 124. In an embodiment, surface 205may include a recess 208 located near or adjacent a center of thesurface 205, and the outlet 234 may be disposed in the recess 208.Alternatively, the inlet passage 230 may be disposed in the jacket 122rather than the manifold 200, and may fluidly connect to the inlet line30 to direct fluid from the inlet line 30 to the reservoir 124 containedin the jacket 122.

The inlet passage 230 may be formed by one or more linear bores (e.g.,extending along a generally straight line). For example, the inletpassage 230 may be formed by drilling a first linear bore to a desiredlength into the base 212 starting at the desired location of the inlet232 and drilling a second linear bore into the raised portion 204starting at the desired location of the outlet 234 until the secondlinear bore intersects the first linear bore. The first linear bore thatforms the inlet 232 may extend radially toward the center of the base212 and between a pair of adjacent mounting bores 216. Alternatively,the second linear bore may be drilled to a desired length and then thefirst linear bore may be drilled until the first linear bore intersectsthe second linear bore. By drilling the linear bores until theyintersect, the inlet passage 230 may be formed without creating extraholes in the outer surface of the manifold 200, which may need to beplugged. As a result, the time and cost to form the manifold 200 may bereduced.

The discharge passage 240 may include one or more inlets 242 that may befluidly connected to the pumping mechanisms 300 so that the inlet(s) 242may receive fuel pumped from the pumping mechanisms 300. In theexemplary embodiment, the discharge passage 240 has five inlets 242corresponding to the number of pumping mechanisms 300, but it isunderstood that there may be more or fewer than five inlets 242,depending on the number of pumping mechanisms 300 in the pump 100. Theinlets 242 may be disposed in surface 205 as described below to receivefuel pumped by the pumping mechanisms 300, which are mounted ontosurface 205. The inlets 242 may be disposed farther from the center ofsurface 205 (and/or the center of the raised portion 204) than theoutlet 234 of the inlet passage 230. As shown in FIG. 3, the inlets 242may also be disposed radially around the recess 208 and/or the center ofthe surface 205 (and/or the center of the raised portion 204), e.g.,radially spaced at generally equal intervals.

The discharge passage 240 may also include a common outlet 244 fluidlyconnected to discharge the high-pressure fuel received from the inlets242 out of the pump 100. The outlet 244 may be fluidly connected to thedischarge line 40 so that the outlet 244 may direct the pumped fuel tothe engine 12. In the embodiment shown in FIGS. 2 and 3, the outlet 244may be disposed on the peripheral surface 220 of the manifold 200.Alternatively, the outlet 244 may be disposed on any surface of themanifold 200 outside surface 205, such as surface 214.

The discharge passage 240 may also include a plurality of connectingbranches 246 that fluidly connect the inlets 242 to a common outletbranch 248 in a tree-shaped configuration. The inlets 242 and theconnecting branches 246 may connect in parallel to the outlet branch248. The outlet branch 248 may combine the flow of fuel from theconnecting branches 246 and direct the combined flow to the outlet 244.Each of the connecting branches 246 and the outlet branch 248 may beformed by linear bores. For example, the outlet branch 248 may be formedby drilling a linear bore into the base 212 of the manifold 200 startingat the desired location of the outlet 244 on the peripheral surface 220until reaching a desired length of the outlet branch 248. The linearbore forming the outlet branch 248 may extend radially toward the centerof the base 212 and between a pair of adjacent mounting bores 216. Eachof the connecting branches 246 may be formed by drilling a linear boreinto the raised portion 204 starting at the desired location of therespective inlet 242 on surface 205 until the linear bore intersects theoutlet branch 248. Alternatively, the connecting branches 246 may bedrilled to a desired length and then the outlet branch 248 may bedrilled until the bore intersects each connecting branch 246. Bydrilling the linear bores until they intersect, the discharge passage240 may be formed without creating extra holes in the outer surface ofthe manifold 200, which may need to be plugged. In addition, theconnecting branches 246 may be formed perpendicular to the outlet branch248 when viewed from the top view of FIG. 3. As a result, the time andcost to form the manifold 200 may be reduced, and the flow path for thehigh-pressure fuel may be relatively more direct and less complex.

The leakage passage 250 may fluidly connect to the push rod guide bores206 to receive fuel, e.g., liquid and/or gaseous fuel, leaking from thepumping mechanisms 300 mounted to the manifold 200. The leakage passage250 may include a common outlet 254 that may be fluidly connected to theleakage line 50 to direct the leaked fuel from the pumping mechanisms300 back to the storage tank 14. In the embodiment shown in FIGS. 2 and3, the outlet 254 may be disposed on the peripheral surface 220 of themanifold 200. Alternatively, the outlet 254 may be disposed on anysurface of the manifold 200 outside surface 205, such as surface 214.

The leakage passage 250 may include connecting branches 256 that fluidlyconnect the push rod guide bores 206 in a daisy chain configuration toform a loop. The connecting branches 256 may include inlets that fluidlyconnect to the respective push rod guide bores 206. The push rod guidebores 206 and the connecting branches 256 may be disposed farther fromthe center of surface 205 (and/or the center of the raised portion 204)than the outlet 234 of the inlet passage 230 and/or the inlets 242 ofthe discharge passage 240. As shown in FIG. 3, the push rod guide bores206 may also be disposed radially around recess 208, the center ofsurface 205 (and/or the center of the raised portion 204), and/or theinlets 242, e.g., radially spaced at generally equal intervals. In theexemplary embodiment, the leakage passage 250 has five connectingbranches 256 corresponding to the five push rod guide bores 206, whichcorresponds to the number of pumping mechanisms 300, but it isunderstood that there may be more or fewer than five connecting branches256, depending on the number of pumping mechanisms 300 in the pump 100.

The leakage passage 250 may also include an outlet branch 258 thatfluidly connects to one of the connecting branches 256 forming the loop.The outlet branch 258 may direct the flow of leaked fuel from the loopof connecting branches 256 to the outlet 254. Each of the connectingbranches 256 and the outlet branch 258 may be formed by linear bores.For example, each of the connecting branches 256 may be formed bydrilling a first linear bore to a desired length into the raised portion204 starting at one of the push rod guide bores 206 and drilling asecond linear bore into the raised portion 204 starting at the adjacentpush rod guide bore 206 until the second linear bore intersects thefirst linear bore. Each push rod guide bore 206, or at least the endthereof, may have a sufficient width to allow the first and secondlinear bores to be drilled at an angle so that the first and secondlinear bores intersect to form an apex in the middle of the connectingbranch 256. The outlet branch 258 may be formed by drilling a linearbore into the base 212 of the manifold 200 starting at the desiredlocation of the outlet 254 on the peripheral surface 220 untilintersecting one of the connecting branches 256. The linear bore formingthe outlet branch 258 may extend radially toward the center of the base212 and between a pair of adjacent mounting bores 216. Alternatively,the outlet branch 258 may be drilled to a desired length and then theconnecting branches 256 may be drilled such that one of the connectingbranches 256 intersects the outlet branch 258. By drilling the linearbores until they intersect, the leakage passage 250 may be formedwithout creating extra holes in the outer surface of the manifold 200,which may need to be plugged. As a result, the time and cost to form themanifold 200 may be reduced.

The bypass passage 260 may include an inlet 262 that may extend throughsurface 205 so that fuel, e.g., liquid fuel, may be directed from thereservoir 124 back to the storage tank 14, as will be described below.The inlet 262 may extend through surface 205 and may be located fartherfrom the center of surface 205 (and/or the center of the raised portion204) than the outlet 234 of the inlet passage 230, the inlets 242 of thedischarge passage 240, the push rod guide bores 206, and/or theconnecting branches 256 of the leakage passage 250.

The bypass passage 260 may also include an outlet 264 that may befluidly connected to the bypass line 60 to direct the fuel from thereservoir 125 to the storage tank 14. The outlet 264 may be disposed onthe peripheral surface 220 of the manifold 200, as shown in FIGS. 2, 3,and 5. Alternatively, the outlet 264 may be disposed on any surface ofthe manifold 200 outside surface 205, such as surface 214.

The bypass passage 260 may be formed by one or more linear bores. Forexample, the bypass passage 260 may be formed by drilling a first linearbore to a desired length into the base 212 starting at the desiredlocation of the outlet 264 and drilling a second linear bore into theraised portion 204 starting at the desired location of the inlet 262until the second linear bore intersects the first linear bore. The firstlinear bore that forms the outlet 264 may extend radially toward thecenter of the base 212 and between a pair of adjacent mounting bores216. Alternatively, the second linear bore may be drilled to a desiredlength and then the first linear bore may be drilled until the firstlinear bore intersects the second linear bore. By drilling the linearbores until they intersect, the bypass passage 260 may be formed withoutcreating extra holes in the outer surface of the manifold 200, which mayneed to be plugged. As a result, the time and cost to form the manifold200 may be reduced.

The linear bores that form the inlet 232 of the inlet passage 230, theoutlet 254 of the leakage passage 250, the outlet 264 of the bypasspassage 260, and the outlet 244 of the discharge passage 240 may extendbetween different pairs of the plurality of mounting bores 216.

As shown in FIGS. 4-6, each pumping mechanism 300 may include a barrelassembly 310 including a base or proximal end 312 and a distal end 314opposite the proximal end 312. The terms “proximal” and “distal” areused herein to refer to the relative positions of the components of theexemplary barrel assembly 310. When used herein, “proximal” refers to aposition relatively closer to the end of the barrel assembly 310 thatconnects to the manifold 200. In contrast, “distal” refers to a positionrelatively further away from the end of the barrel assembly 310 thatconnects to the manifold 200.

A majority of the outer surface of the barrel assembly 310 may begenerally cylindrical and may have a longitudinal axis 316 extendingbetween the proximal end 312 and the distal end 314. The barrel assembly310 may include a generally hollow barrel 318 formed at the proximal end312 and a head 340 formed at the distal end 314. The head 340 may beattached to the barrel 318 to close off the barrel 318. Alternatively,the barrel assembly 310, including the barrel 318 and the head 340, maybe formed integrally as a single component.

A plunger bore 320 may extend through the barrel 318 and may beconfigured to receive a plunger 330 for sliding within the plunger bore320. A distal end of the plunger bore 320 may form a chamber 322, whichmay extend into the head 340. A proximal end of the plunger bore 320 mayalso align with the push rod guide bores 206 in the manifold 200 suchthat the plungers 330 may slide proximally into at least a portion ofthe push rod guide bores 206. The plunger bore 320 may extend generallyparallel to the axis 316 of the barrel assembly 310. The plunger bore320 may have an axis that is collinear with the axis 316 of the barrelassembly 310, which may be collinear with an axis of the barrel 318.

The plunger 330 may include a main portion 332, a distal portion 334,and may form a shoulder 336 at the transition between the main portion332 and the distal portion 334. The shoulder 336 may be angled as shownin FIG. 5, or may form a step, curve, or other shape. The cross-sectionof the main portion 332 may be sized with respect to the cross-sectionof the plunger bore 320 such that the main portion 332 may slide withinthe plunger bore 320 without damaging the plunger bore 320 or theplunger 330. In the embodiment shown in FIG. 5, the chamber 322 at thedistal end of the plunger bore 320 may have a lateral dimension (e.g.,an inner diameter or width) that is smaller than a lateral dimension ofthe proximal end of the plunger bore 320 through which the main portion332 slides. The plunger bore 320 may form a transition portion 324 (FIG.5) at the transition between the smaller lateral dimension of thechamber 322 and the larger lateral dimension of the proximal end of theplunger bore 320. As shown in FIG. 5, the transition portion 324 may beformed with a chamfer or angled edge to correspond to the angledshoulder 336 of the plunger 330, or alternatively may form a step,curve, or other shape. In an embodiment, the chamber 322 having thesmaller lateral dimension may be disposed in the head 340, and theproximal end of the plunger bore 320 having the larger lateral dimensionmay be disposed in the barrel 318.

The angled edge of the transition portion 324 of the plunger bore 320may have an angle α (FIG. 5) that is different from an angle β of theshoulder 336 of the plunger 330. The difference in angles (angledifferential) may be approximately 3° to 6°. For example, in anembodiment, the angled edge of the transition portion 324 of the plungerbore 320 may be formed at an angle α of approximately 40° relative tothe axis 316 of the barrel assembly 310, and the shoulder 336 of theplunger 330 may be formed at an angle β of approximately 45° relative tothe axis of the plunger 330 (which may be collinear with the axis 316 ofthe barrel assembly 310), thereby resulting in an angle differential(e.g., the difference between angle a and angle β) of approximately 5°.Providing the angle differential may assist in preventing the plunger330 from wedging into and sticking in the plunger bore 320 if the distalportion 334 of the plunger 330 slides into the chamber 322.Alternatively, the angle α of the angled edge of the transition portion324 may be substantially equal to the angle β of the shoulder 336.

The cross-section of the distal portion 334 of the plunger 330 may besized with respect to the cross-section of the chamber 322 such that thedistal portion 334 may slide within the chamber 322 without damaging theplunger bore 320 or the plunger 330. The distal portion 334 may have alateral dimension (e.g., outer diameter or width) that is smaller than alateral dimension of the main portion 332. Alternatively, the chamber322 and the distal portion 334 of the plunger 330 may have the same sizeand cross-section as the proximal end of the plunger bore 320 and themain portion 332 of the plunger 330, respectively.

The head 340 may include at least one inlet passage 342 fluidlyconnected to the plunger bore 320 and configured to receive fuel fromthe reservoir 124. In the exemplary embodiment, the head 340 has fourinlet passages 342 disposed radially around the axis 316, e.g., radiallyspaced at generally equal intervals, but it is understood that there maybe more or fewer than four inlet passages 342. Each inlet passage 342may include an inlet adjacent to the distal end 314 and an outletfluidly connected to the plunger bore 320 so that the plunger bore 320receives fuel from the reservoir 124 via the inlet passages 342. Forexample, the inlet of each inlet passage 342 may extend through thedistal end 314.

The reservoir 124 may receive fuel pressurized by the boost pump 16 viathe inlet line 30 and the inlet passage 230 in the manifold 200. Thereservoir 124 may be completely or nearly completely filled with liquidfuel during a pumping operation. Accordingly, the outer surface of thebarrel assembly 310, e.g., the outer surfaces of the barrel. 318 and thehead 340, may be at least partially submerged within the liquid fuelduring operation. Fuel may surround at least a portion of the outersurface of the barrel assembly 310 at the distal end 314. For example,at least the distal end of the head 340 (e.g., at least the inlets ofthe inlet passages 342) may be located a distance below a liquid surfaceinside the reservoir 124. The pump 100 may normally be packaged for usein the orientation shown in FIGS. 1 and 4-6, such that the manifold 200may cover an opening of the jacket 122 to form the reservoir 124.Therefore, the manifold 200 may form a ceiling of the reservoir 124, andthe jacket 122 may constitute a floor and walls thereof.

Each push rod 114 may extend through the push rod guide bores 206 in themanifold 200 into a corresponding barrel 318. For example, each push rod114 may include a distal end 116 that may contact and push the plunger330 distally within the plunger bore 320. The push rod 114 may separateand move away from the plunger 330, as will be described below.

The barrel 31$ and the head 340 may also form an outlet passage 350fluidly connected to the plunger bore 320 and configured to receive fuelfrom the plunger bore 320. The inlet passages 342 and the outlet passage350 may open into the chamber 322 such that flow into and out of thechamber 322 may be controlled by an inlet check valve 344 and an outletcheck valve 352 described below.

During normal operation of the pump 100, the plunger 330 may slidebetween a Bottom-Dead-Center position (BDC) and a Top-Dead-Center (TDC)position within the plunger bore 320. The head 340 may house valveelements that facilitate fuel pumping during the movement of the plunger330 between BDC and TDC positions. In an embodiment, the head 340 mayinclude the inlet check valve 344 associated with the inlet flow fromthe inlet passages 342, and the outlet check valve 352 associated withoutlet flow to the outlet passage 350. Thus, the inlet passages 342 arefluidly connected to the plunger bore 320 via the inlet check valve 344.

Due to the undulation of the load plate 112 during normal operation ofthe pump 100, the push rod 114 may move away and be spaced from theplunger 330 (upward movement in FIGS. 4 and 5). Due to the difference inpressure between the distal and proximal ends of the plunger 330, theplunger may move from TDC to BDC (upward movement in FIGS. 4 and 5).Specifically, pressurized fuel from the boost pump 16 (via the inletline 30 and the reservoir 124) may unseat an element of the inlet checkvalve 344, allowing the fuel to be directed into the plunger bore 320.The pressure acting on the distal end of the plunger 330 is generallyequal to the boost pressure of the pressurized fuel pumped from theboost pump 16 (via the inlet line 30), and the pressure acting on theproximal end of the plunger 330 is generally equal to the relativelylower tank pressure of the fuel stored in the storage tank 14 (via theleakage line 50). The pressure differential causes the plunger to movefrom TDC to BDC. Thus, the boost pump 16 provides pressure sufficient tolift the plunger 330.

The undulation of the load plate 112 may also cause the push rod 114 tomove toward and push against the proximal end of the plunger 330(downward movement in FIGS. 4 and 5). During the ensuing plungermovement from BDC to TDC (downward movement in FIGS. 4 and 5), highpressure may be generated within the plunger bore 320 by the volumecontracting inside the plunger bore 320. This high pressure may functionto reseat the element of the inlet check valve 344 and unseat an elementof the outlet check valve 352, allowing fuel from within the plungerbore 320 to be pushed out through the outlet passage 350. Then duringthe next plunger movement from TDC to BDC, the element of the outletcheck valve 352 may be reseated. One or both of the elements of theinlet check valve 344 and the outlet check valve 352 may bespring-biased to a particular position, if desired (e.g., toward theirseated and closed positions). The fuel may be discharged from theplunger bore 320 through the outlet passage 350, and the pressurizedfuel from the outlet passages 350 of all of the pumping mechanisms 300may be combined in the discharge passage 240 in the manifold 200 fordischarge from the pump 100 via discharge line 40.

During normal operation of the pump 100, the plunger 330 and/or theplunger bore 320 may be configured so that the plunger 330 does notslide far enough within the plunger bore 320 to contact the transitionportion 324 when the plunger 330 moves from BDC to TDC. If the plunger330 does slide far enough to contact the transition portion 324, thetransition portion 324 may prevent the plunger 330 from contacting theinlet check valve 344. The shoulder 336 of the plunger 330 may abutagainst the transition portion 324 to prevent the plunger 330 fromsliding too far into the chamber 322.

Further, the length of the distal portion 334 of the plunger 330 alongthe axis 316 and the length of the chamber 322 along the axis 316 may beconfigured so that the distal portion 334 and the inlet check valve 344are far enough away from each other to avoid overlap between the normalranges of motion of the plunger 330 and the inlet cheek valve 344. Therespective lengths of the distal portion 334 and the chamber 322 mayalso be configured so that the distal portion 334 and the inlet checkvalve 344 are close enough to each other to minimize the volume in thechamber 322. For each stroke of the plunger 330 during normal operationof the pump 100, the chamber 322 may contain an amount of fuel that ispressurized by the pumping mechanism 300, but is not discharged throughthe outlet check valve 352 into the outlet passage 350. The energy usedto pump the fuel contained in the chamber 322 may be wasted. Therefore,minimizing the volume of the chamber 322 may minimize the amount ofenergy wasted by the pump 100. Also, the fuel in the chamber 322 may bewarmer and may transfer heat to the fuel in the next stroke. Warmer fuelmay be less viscous, which may then result in more fuel leaking into theleakage passage 250 and a reduction in pump efficiency. Warmer fuel mayalso be less dense, which may also result in a reduction in pumpefficiency.

Fuel may leak past the plungers 330 into the proximal ends of therespective plunger bores 320 due to the pressure differential betweenthe pressure acting on the distal end of the plunger 330 and thepressure acting on the proximal end of the plunger 330. The proximalends of the plunger bores 320 may be fluidly connected to the respectivepush rod guide bores 206, which may direct the leaked fluid to theleakage passage 250 in the manifold 200. The leaked fuel from each ofthe pumping mechanisms 300 may be combined in the leakage passage 250and directed back to the storage tank 14 via leakage line 50, asdescribed above.

The outlet passage 350 may be separate from the plunger bore 320 suchthat the plunger bore 320 and the outlet passage 350 form separateopenings in the proximal end 312 of the barrel assembly 310. In anembodiment, the outlet passage 350 may include a first portion 354 and asecond portion 356. The outlet check valve 352 may be disposed in thefirst portion 354, and the second portion 356 may receive fuel from thefirst portion 354 via the outlet check valve 352. The first portion 354may extend from the plunger bore 320 toward the distal end 314 of thebarrel assembly 310 at an acute angle with respect to axis 316. Thesecond portion 356 may be generally parallel to the plunger bore 320 andmay form the opening of the outlet passage 350 adjacent to the proximalend 312 of the barrel 318. For example, the opening of the outletpassage 350 may form the outlet of the outlet passage 350 and may extendthrough the proximal end 312 of the barrel 318. The second portion 356may be located closer to the outer surface of the barrel assembly 310(e.g., the outer surface of the barrel 318 and the head 340) than theplunger bore 320.

The pumping mechanisms 300 may be mounted in a radial configuration onthe manifold 200, e.g., radially spaced with respect to axis 110. Forexample, the barrel assemblies 310 may be spaced at generally equalintervals around axis 110 and at a radial distance R (FIG. 4) withrespect to axis 110. To mount each pumping mechanism 300 to the manifold200, the barrel assembly 310 may include one or more mounting bores 360configured to receive one or more fasteners 362. In the exemplaryembodiment, the barrel assembly 310 has five mounting bores 360configured to receive five fasteners 362, but it is understood thatthere may be more or fewer than five mounting bores 360 and fasteners362. The mounting bores 360 may extend from the proximal end 312 to thedistal end 314 of the barrel assembly 310, and may be generally parallelto the plunger bore 320 and the second portion 356 of the outlet passage350. Each barrel assembly 310 may include a boss or other protrusion inwhich the outlet check valve 352 is disposed, and which extends from thehead 340, as shown in FIGS. 1 and 4-6. The boss may extend generallyradially outward from the axis 316 of the barrel assembly 310 anddistally from the distal end 314. Also, to reduce the possibility forinterference, each barrel assembly 310 may be rotated by about 15° orless so that the bosses may extend at an angle with respect to the line,connecting the axes 110 and 316 instead of pointing directly toward axis110 of the pump 100.

INDUSTRIAL APPLICABILITY

The disclosed fluid system and pump finds potential application in anyfluid system where heat transfer to the fluid is undesirable and wherepriming of the pump is desired. The disclosed pump finds particularapplicability in cryogenic applications, for example power systemapplications having engines that burn LNG fuel. One skilled in the artwill recognize, however, that the disclosed pump could be utilized inrelation to other fluid systems that may or may not be associated with apower system. Operation of the fluid system 10 and the pump 100 will nowbe explained.

Priming of the pump 100 may occur when the engine 12 is stopped oroperating in a mode that does not depend on high-pressure fuel from thepump 100, such as a diesel-only operating mode or a low-pressure gasspark-ignited operating mode. Priming of the pump 100 may be desired,for example, when the pump 100 is started after being inactive for anextended period of time. Due to the inactivity, the pump 1.00 may warmto temperatures that are less desirable for operation of the pump 100,e.g., up to ambient temperatures. Therefore, priming of the pump 100 maybe desirable to cool the pump 100 to a desirable operating temperaturebefore the pump 100 may be started at normal operation to supplyhigh-pressure fuel to the engine 12. As a result, the likelihood of apump failure due to thermal gradients in the pump 100 may be reduced.Also, the pump 100 may not operate as efficiently or at all if one ormore of the components in the pump 100 are too hot. The heat may causefuel in the pump 100 to vaporize and prevent the build-up of pressure inthe chamber 322.

The pump 100 may be cooled by allowing flow to circulate through thepump 100 using the inlet line 30, the discharge line 40, the leakageline 50, and the bypass line 60. To begin priming the pump 100, theboost pump 16 may be started. Referring to FIG. 1, the boost pump 16 maysupply fuel pressurized to a boost pressure from the storage tank 14into the reservoir 124 via the inlet line 30. During priming, the powersource (e.g., the electric motor) for rotating the driveshaft 104 mayremain shut down and inactive. As a result, the push rods 114 may alsobe inactive and held in position so that they do not push the plungers330, thereby causing the plungers 330 to be inactive.

Fuel pressurized by the boost pump 16 may flow from the reservoir 124(e.g., through the inlet passages 342 and past the inlet check valves344 in the barrel assemblies 310) into the barrel assemblies 310. Thefuel may then flow from the barrel assemblies 310 (e.g., past the outletcheck valves 352 and through the outlet passages 350 in the barrelassemblies 310) to the discharge passage 240 in the manifold 200 andthen to the discharge line 40. As a result, fuel (including relativelycolder fuel from the storage tank 14 via the inlet line 30 and thereservoir 124) may flow through the inlet passages 342 via the inletcheck valves 344 and through the outlet passages 350 via the outletcheck valves 352 in the barrel assemblies 310 to assist in cooling theinside of the barrel assemblies 310.

Further, because relatively colder fuel from the storage tank 14 isentering the reservoir 124 via the inlet line 30, the colder fuel mayflow around the barrel assemblies 310 to cool the outside of the barrelassemblies 310. Also, the second portions 356 of the outlet passages 350may be located closer to the outer surfaces of the respective barrelassemblies 310 than the plunger bore 320. As a result, the colder fuelflowing around the barrel assemblies 310 may cool the second portions356 of the outlet passages 350.

In the discharge line 40, the heater 42 may beat the liquid to gaseousfuel, which may be stored in the accumulator 44. The gaseous fuel may bestored in the accumulator 44, and a valve (not shown) in the dischargeline 40 may be closed to prevent the gaseous fuel from being supplied tothe engine 12.

When priming begins the pressure in the outlet passages 350 of thebarrel assemblies 310 may be less than the boost pressure of the fuelsupplied by the boost pump 16. As fuel flows from the reservoir 124through the barrel assemblies 310 during priming, the pump 100 maydirect fuel to the accumulator 44 until the pressure in the outletpassage 350 and/or the discharge passage 240 in the barrel assemblies310 is substantially equal to the boost pressure, e.g., the pressure ofthe fluid in the reservoir 124. The pressures may be substantially equalwhen enough fuel accumulates downstream of the pump 100 to limit or stopadditional fuel from flowing into the outlet passage 350. The fuel mayaccumulate in lines or passages downstream from the outlet passage 350,such as the discharge passage 240, lines or passages fluidly connectingthe pump 100 to the engine 12 (e.g., the discharge line 40 and/or theaccumulator 44, if included in the fluid system 10), and/or lines orpassages in the engine 12. The range of pressures that are considered“substantially equal” to the boost pressure may include pressures thatare slightly less than the boost pressure and that result in stoppingfuel flow into the outlet passage 350. When the pressures aresubstantially equal, the outlet check valves 352 in the barrelassemblies 310 may close, thereby limiting or preventing fuel fromflowing into the outlet passages 350.

Excess liquid and/or vapor inside the reservoir 124 may be returned tothe storage tank 14 via the bypass passage 260 in the manifold 200 andthe bypass line 60, e.g., to maintain a desired pressure within thereservoir 124, as shown in FIG. 6. In this way, regardless of the usagerate of the fluid from the reservoir 124 and/or the supply rate of fluidto the reservoir 124, the reservoir 124 may not be overfilled with fluidand the resulting pressure may be maintained at a desired level. Theregulating valve 62 (or orifice) in the bypass line 60 may control theamount of flow directed to the storage tank 14 from the reservoir 124.For example, the regulating valve 62 may maintain a certain differencein pressure between the storage tank 14 and the reservoir 124.Therefore, the regulating valve 62 may adjust the pressure in the bypassline 60 based on the pressure of the fuel in the storage tank 14. Thefuel may flow into the reservoir 124 via the inlet line 30 and out ofthe reservoir 124 via bypass line 60. As a result, fuel (includingrelatively colder fuel from the storage tank 14 via the inlet line 30and the reservoir 124) may flow around the barrel assemblies 310 andcool the outside of the barrel assemblies 310.

Thus, when priming the pump 100, a first flow of fuel may be directedfrom the reservoir 124 into the discharge passage 240 of via the inletpassages 342 and the outlet passages 350 in the barrel assemblies 310)without pumping the first flow of fuel until the pressure in the outletpassage 350 and/or the discharge passage 240 is substantially equal tothe boost pressure. Also, when priming the pump 100, a second flow offuel may be directed from the reservoir 124 into the bypass passage 260and then returned to the storage tank 14.

During priming, some of the fuel that flows from the reservoir 124 intothe barrel assemblies 310 may leak past the plungers 330 in the plungerbores 320. The leaked fuel may flow through the plunger bores 320 intothe push rod guide bores 206 and the leakage passage 250 in the manifold200, and the leakage line 50 back to the storage tank 14. As a result,the flow of fuel past the plungers 330 in the plunger bores 320(including relatively colder fuel from the storage tank 14 via the inletline 30 and the reservoir 124) may assist in cooling the inside of thebarrel assemblies 310.

After fuel stops flowing into the discharge passage 240 of the pump 100,fuel may continue to flow into the reservoir 124 via the inlet line 30and out of the reservoir 124 via bypass line 60 for a period of time,e.g., until the temperature of the fuel in the bypass line 60, asmeasured by the sensor 64, drops to a desired temperature, e.g., equalto or less than a threshold temperature. For example, the threshold maybe approximately equal to or within an acceptable difference (e.g., 10°C. or less) from the temperature of the fuel in the storage tank 14. Forexample, if LNG is stored in the storage tank 14 at about 140° C., thedesired temperature may be about 130° C. or less. When the desiredtemperature is reached, priming of the pump 100 may end and normaloperation of the pump 100 may begin. For example, during normaloperation of the pump 100, a pump controller (not shown) may start thepower source (e.g., the electric motor), which may start up the drivemechanism (e.g., the driveshaft 104 and the load plate 112) configuredto cause the plungers 330 to cyclically rise and fall within the barrelassemblies 310, and then the pump 100 may pressurize fuel for directingto the engine 12. The valve (not shown) in the discharge line 40 may beopened to allow the gaseous fuel to be injected into the engine 12.

In an embodiment, flow may be directed from the reservoir 124 to thestorage tank 14 continuously via the regulating valve 62 (or orifice) inthe bypass line 60 during priming and normal operation of the pump 100.Alternatively, the regulating valve 62 may be closed when priming ends(e.g., when the desired temperature is reached) and may remain closedduring normal operation of the pump 100.

During normal operation of the pump 100, the driveshaft 104 may berotated by the power source (e.g., the electric motor), which may causethe load plate 112 to undulate in an axial direction. This undulationmay result in translational movement of the push rods 114. As describedabove, the rotation of the driveshaft 104 in combination with the supplyof fuel at boost pressure into the pumping mechanisms 300 may causeaxial movement of the plungers 330 between TDC and BDC. Alternatively,other drive mechanisms may be provided, in place of the driveshaft 104and the load plate 112, to cause the push rods 114 to movetranslationally.

As the plungers 330 cyclically rise and fall within the barrelassemblies 310, this reciprocating motion may function to allow liquidto flow from the reservoir 124 (e.g., through the inlet passages 342 andpast the inlet check valves 344 in the barrel assemblies 310) into thebarrel assemblies 310 and to push the fluid from the barrel assemblies310 (e.g., past the outlet check valves 352 and through the outletpassages 350 in the barrel assemblies 310) at an elevated pressure. Thehigh-pressure liquid may flow through the outlet passages 350 of thebarrel assemblies 310, the discharge passage 240 in the manifold 200,and the discharge line 40 to be injected into the engine 12. Thepressure of the fluid that is output from the pump 100 via the dischargeline 40 may be greater than the pressure of the fluid supplied from theboost pump 16.

The manifold 200 may be formed as a single integral component thatallows different paths of fluid flow to be routed between the reservoir124, the storage tank 14, and the accumulator 44 or the engine 12without individual lines, seals, clamps, or other components for formingthe fluid connections during priming and normal operation of the pump100. The passages in the manifold 200, such as the inlet passage 230,the discharge passage 240, the leakage passage 250, and the bypasspassage 260, may be formed using intersecting linear bores that arepositioned to avoid having to use plugs to prevent leakage from thepassages, as described above. Also, the linear bores of the inletpassage 230, the discharge passage 240, the leakage passage 250, and thebypass passage 260 may be positioned to avoid intersections between thedifferent passages and to provide a design that may be easier tomanufacture. Also, fuel flowing through the passages in the manifold 200may assist in cooling the manifold and therefore the pump 100.

The barrel assemblies 310 may be disposed in the pump 100 to provide amore compact design that may be less susceptible to failure due tothermal stresses. For example, flow may be discharged from the barrelassemblies 310 via the respective outlet passages 350, which may bedisposed in the barrel assemblies 310 parallel to the plunger bores 320,instead of as individual lines or pipes that are external and connectedto the barrel assemblies 310. External pipes may have minimum bend radiirequirements, which may cause the external pipes to take up more space.External pipes may also experience pressure waves, which may cause thepipes to vibrate and leak. Without external pipes, the barrel assemblies310 may be formed with a lower overall number of connections and shorterroutes for the fuel, and may provide a uniform and symmetric geometrythat reduces thermal gradients. Also, the design of the barrelassemblies 310 may be relatively compact and may allow for a relativelysmaller radial distance R for the barrel assemblies 310. As a result,the overall size of the pump 100 may be smaller.

In addition, without external pipes, less surface area may be exposed tothe fuel in the reservoir 124, which may reduce heat transfer from theoutlet passages 350 in the barrel assemblies 310 to the fuel in thereservoir 124. The outlet passages 350 may receive fuel that may berelatively warmer during normal operation of the pump 100 than the fuelin the reservoir 124.

The plungers 330 may be sealless, and at least the main portions 332 ofthe plungers 330 may have a uniform outer dimension (e.g., the outerdiameter). The plungers 330 may also be formed as a single integralcomponent, and a tight clearance may be formed between the plungers 330and the respective plunger bores 320. The plungers 330 may be formedwithout an external seal (e.g., a piston seal, such as a plastic ornon-metallic component disposed on the outer surface of the plunger330), which may wear and limit the life of the pump 100. Alternatively,the plungers 330 may include the external seal or other type of seal.The plungers 330 may be connected to or disconnected from the distalends 116 of the push rods 114. When the plungers 330 are not connectedto the push rods 114, any side forces on the plungers 330 from the pushrods 114 may be reduced or eliminated. This may reduce or eliminatewear, scuffing, and other damage on the plungers 330 and the plungerbores 320.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the pump of the presentdisclosure. Other embodiments of the fluid system and the pump will beapparent to those skilled in the art from consideration of thespecification and practice of the fluid system and the pump disclosedherein. It is intended that the specification and examples be consideredas exemplary only, with a true scope being indicated by the followingclaims and their equivalents.

What is claimed is:
 1. A pumping mechanism comprising: a barrel assemblyincluding a plunger bore, the plunger bore having a longitudinal axis; aplunger configured to slide within the plunger bore parallel to thelongitudinal axis; and a push rod separate from the plunger, the pushrod being configured to move away from the plunger to be spaced from theplunger, the push rod being further configured to move within theplunger bore to push the plunger.
 2. The pumping mechanism of claim 1,wherein: the plunger is configured to slide in a first direction alongthe longitudinal axis and a second direction opposite the firstdirection along the longitudinal axis; and the push rod is configured tomove away from the plunger to allow the plunger to move in the firstdirection and to push the plunger in the second direction.
 3. Thepumping mechanism of claim 2, wherein the plunger bore is configured toreceive a flow of pressurized fluid to push the plunger in the firstdirection.
 4. The pumping mechanism of claim 3, further including aninlet check valve configured to control flow directed into the plungerbore to push the plunger in the first direction.
 5. The pumpingmechanism of claim 3, further including an outlet check valve configuredto control at least a first portion of the flow of pressurized fluiddirected from the plunger bore to an outlet passage in the barrelassembly, the outlet passage having at least a portion that is generallyparallel to and separate from the plunger bore.
 6. The pumping mechanismof claim 5, wherein the plunger bore is configured to supply a secondportion of the flow of pressurized fluid out of the barrel assembly fromthe plunger bore, the second portion being separate from the firstportion of the flow of pressurized fluid.
 7. The pumping mechanism ofclaim 1, wherein: the plunger bore includes a proximal end, a distal endhaving a lateral dimension that is smaller than a lateral dimension ofthe proximal end, and a transition portion formed at a transitionbetween the proximal end and the distal end of the plunger bore; theplunger includes a main portion, a distal portion having a lateraldimension that is smaller than a lateral dimension of the main portion,and a shoulder formed at a transition between the main portion and thedistal portion; and the shoulder of the plunger is configured to abutagainst the transition portion to limit movement of the plunger into thedistal end of the plunger bore.
 8. The pumping mechanism of claim 7,wherein: the transition portion has an edge that is angled with respectto the longitudinal axis, and the shoulder is angled with respect to thelongitudinal axis; and an angle differential between an angle of theedge of the transition portion and an angle of the shoulder isapproximately 3° to 6°.
 9. The pumping mechanism of claim 1, wherein theplunger is sealless.
 10. A pump comprising: a reservoir configured tostore a fluid; and at least one pumping mechanism at least partiallydisposed in the reservoir, the at least one pumping mechanism including:a barrel assembly including a plunger bore, the plunger bore having alongitudinal axis and being fluidly connected to the reservoir, aplunger configured to slide within the plunger bore along thelongitudinal axis in a first direction and in a second directionopposite the first direction, and a push rod separate from the plunger,the push rod being configured to move away from the plunger to allow theplunger to move in the first direction, the push rod being furtherconfigured to move within the plunger bore to push the plunger in thesecond direction to direct the fluid to a discharge passage of the pump.11. The pump of claim 10, wherein the plunger bore is configured toreceive a flow of pressurized fluid to push the plunger in the firstdirection.
 12. The pump of claim 10, wherein the barrel assemblyincludes an outlet check valve configured to control an amount of thefluid directed into the discharge passage of the pump.
 13. The pump ofclaim 12, wherein the push rod is configured to push the plungerdistally in the plunger bore along the longitudinal axis to direct thefluid past the outlet check valve toward the discharge passage.
 14. Thepump of claim 10, wherein the barrel assembly includes an inlet checkvalve configured to control an amount of the fluid entering the plungerbore from the reservoir, and the plunger is configured to move in thefirst direction in the plunger bore when a pressurized fluid is directedto the plunger bore via the inlet check valve.
 15. A fluid systemcomprising: a storage tank configured to store a fluid; a pump fluidlyconnected to the storage tank to receive the fluid; a boost pumpconfigured to pressurize the fluid to communicate the fluid from thestorage tank into the pump; wherein the pump includes; a reservoirconfigured to store the fluid pressurized by the boost pump; and atleast one pumping mechanism at least partially disposed in thereservoir, the at least one pumping mechanism including: a barrelassembly including a plunger bore, the plunger bore having alongitudinal axis and being fluidly connected to the reservoir, aplunger configured to slide within the plunger bore along thelongitudinal axis in a first direction and in a second directionopposite the first direction, and a push rod separate from the plunger,the push rod being configured to move away from the plunger to allow theplunger to move in the first direction due to a pressure from the fluidpressurized by the boost pump, the push rod also being configured tomove within the plunger bore to push the plunger in the second directionto direct the fluid to a discharge passage of the pump.
 16. The fluidsystem of claim 15, wherein the barrel assembly includes an inlet checkvalve configured to control an amount of the fluid entering the plungerbore from the reservoir.
 17. The fluid system of claim 16, wherein theinlet check valve is configured to close when the plunger slides in thesecond direction.
 18. The fluid system of claim 15, wherein the barrelassembly includes an outlet check valve configured to control an amountof the fluid directed to the discharge passage of the pump.
 19. Thefluid system of claim 15, wherein the plunger bore includes an inletconfigured to receive the fluid pressurized by the boost pump and anoutlet configured to direct fluid leaking between the plunger and theplunger bore back to the storage tank.
 20. The fluid system of claim 19,wherein the plunger is configured to slide in the first direction due toa pressure differential between a pressure acting on a distal end of theplunger and a pressure acting on a proximal end of the plunger, thepressure acting on the distal end of the plunger being generally equalto the pressure of the fluid pressurized by the boost pump, the pressureacting on the proximal end of the plunger being generally equal to apressure of the fluid in the storage tank.